A large display apparatus is known, in which a number of luminescent display cells having so-called phosphor trios formed of, for example, three colors of red, green and blue phosphor segments are arranged in a two-dimensional manner to thereby produce a large picture screen. In this display apparatus, the luminescent display cells are illuminated stably at high brightness, whereby a clear picture of sufficient brightness can be reproduced even outdoors.
Conventionally, such a luminescent display cell 6 is constructed as shown in FIG. 7. That is, three phosphor segments 2R, 2G and 2B which are illuminated in red, green and blue colors are formed on the inner surface of a front panel 1a of a glass housing, and three line-shaped cathodes K (KR, KG and KB) and three first grids (control electrodes) G1 (G1R, G1G and G1B) are formed on a rear panel 1b side in an opposing relation to the respective segments 2R, 2G and 2B. Further, a second grid (accelerating electrode) G2 is provided common to the three first grids G1R, G1G and G1B. A separator 3 formed of a conductive material to which an anode voltage is applied is disposed so as to enclose the respective phosphor segments 2R, 2G and 2B. In this case, in order to independently turn ON and OFF the adjacent phosphor segments 2R, 2G and 2B without cross-talk, the first grids G1R, G1G and G1B are shaped such that mesh-shaped opening portions 4R, 4G and 4B are formed on their cylindrical surfaces so as to encircle the corresponding line-shaped cathodes KR, KG and KB, respectively. The common second grid G2 is shaped as a flat plate configuration which has mesh-like openings 5R, 5G and 5B at its positions corresponding to the first grids G1R, G1G and G1B.
In this luminescent display cell 6, an anode voltage of, for example, about 8 kV is supplied to the phosphor segments 2R, 2G and 2B, a voltage of, for example, 0 V (OFF) to 5 V (ON) is applied to the first grids G1R, G1G and G1B, and a voltage of, for example, about 50 V is applied to the second grid G2. When the voltage of, for example, about 5 V is applied to the first grid G1, an electron beam from the cathode K is traveled through the first grid G1, is accelerated by the second grid G2 and impinges upon the corresponding phosphor segments 2R, 2G and 2B so that these phosphor segments are illuminated. When 0 V is applied to the first grid G1, the electron beam from the cathode K is cut off so that the corresponding phosphor segments are not illuminated. As such luminescent display cell 6, a so-called 8-element display cell, in which 8 sets of red, green and blue phosphor segments of three colors are integrally provided or 2-element display cell or the like is proposed (see Japanese Patent Application No. 60-191703).
Incidentally, in such luminescent display cell, it is requested to simplify its structure. For example, when the luminescent display cell is formed of much more elements, it is preferable that its structure is simplified more from a manufacturing-process standpoint. To this end, it is proposed that the first grid G1, for example, is shaped as a flat plate. If the first grid is simply shaped as a flat plate, the cathode, which should be placed in a cut-off state in the ON-OFF control operation, is affected by the adjacent first grid G1 which is placed in its ON state. As a result, a cross-talk to the adjacent phosphor segment occurs unavoidably. Further, the number of line-shaped cathodes cannot be reduced more than the number of phosphor segments, which provides a serious problem from a manufacturing-process and money standpoint.
In view of the above-mentioned aspect, the present invention is intended to provide a fluorescent display apparatus of simple structure which can be illuminated with high brightness and which can be controlled without cross-talk.